Nitrogen-doped Carbon Materials To Enhance The Productivity Of Anaerobic Fermentation

In the organic wastewater treatment system,anaerobic fermentation transforms the chemical energy of organic compounds into biogas H₂and CH₄,which has been proved to be one of the most economical biogas production methods.However,the traditional anaerobic fermentation still has some shortcomings.In order to make the anaerobic fermentation technology be used as resource on a large scale,it is necessary to strengthen the research of anaerobic fermentation performance,so as to improve the efficiency of anaerobic fermentation degradation of organic matter and production capacity(e.g.,H₂and CH₄).Carbon based materials have been widely used to improve the efficiency of hydrogen and methane production through anaerobic fermentation,including graphite felt,carbon cloth,biochar,activated carbon and carbon nanotubes.It can be used as microbial carrier to promote microbial reproduction and growth.In addition,graphite and activated carbon can promote the direct electron transfer(DIET)of microorganisms in anaerobic fermentation system because of their suitable conductivity.Element doping can improve the physical and chemical properties of carbon materials,such as non-metallic nitrogen,metal elements such as iron,cobalt,nickel,etc.nitrogen can lead to the improvement of electron transfer ability.Carbon nitrogen(NC)bond can optimize the pore structure and increase the interlayer distance of the materials,and improve the electron transfer ability.However,the application of nitrogen doped carbon materials in anaerobic fermentation is rarely reported.Based on the biocompatibility and good electrical conductivity of nitrogen doped carbon materials,it can be predicted as a good additive to enhance anaerobic fermentation.Therefore,in this paper,different nitrogen doped carbon materials were selected as the research object to study their influence mechanism on anaerobic fermentation process.(1)Nitrogen doped biochar(NDBC)and undoped biochar(BC)were prepared from agricultural waste corncob powder by high-temperature pyrolysis,and their effects on hydrogen production by anaerobic fermentation were investigated.Compared with BC directly derived from corncob,NDBC has better fermentative hydrogen production performance.At 600 m L/g NDBC,H₂yield was the highest(230m L/g glucose),which was 64.3%and 44.6%higher than control group(140 m L/g)and BC group(159 m L/g),respectively.NDBC can reduce the abundance of Dysgona and increase the abundance of Clostridium,which is beneficial to produce more hydrogen through butyric fermentation.The NDBC materials rich in nitrogen atoms significantly increase the conductivity,thus promoting the electron transfer in the organism.(2)Nitrogen and phosphorus doped starch derived carbon(NPSC)was successfully prepared by chemical crosslinking method,and the properties of NPSC were characterized.By adding 0-800 mg/L NPSC into a batch anaerobic reactor with glucose as substrate,the effect of NPSC on the performance of mesophilic bio H₂production system was studied.In the dark fermentation process,NPSC can effectively enhance the H₂production.The optimal concentration of starch derived carbon(SC)was 400 mg/L,while the optimal concentration of NPSC was 600 mg/L,which was increased by 35.98%and 61.79%compared with the blank group,respectively;Moreover,the addition of NPSC could affect the microbial community structure and enhance the growth of Clostridium Compared with the control group,the abundance of butyricum increased from 19.09%to 30.87%,which improved the transformation of fermentation pathway to butyric acid fermentation,and increased the utilization rate of substrate,thus further improving the H₂production.(3)Magnetic nitrogen doped activated carbon(NDAC)was prepared by using activated carbon and dicyandiamide as raw materials,under the action of1.10-phenanthroline ethanol solution in oil bath,and then dried in tubular furnace.In the system,the highest hydrogen production(304.58 m L/g glucose)was obtained when the concentration of NDAC was 600 mg/L,which was 51.94%and 20.57%higher than that of blank group and AC group,respectively.Moreover,NDAC has good magnetism and can be recycled.(4)The nitrogen doped biochar(NBC)was prepared from corncob powder,melamine and zinc chloride,and then the magnetic nitrogen doped biochar((Fe-NBC)was prepared by loading magnetite.The effects of two different magnetic nitrogen doped carbon materials,NDAC and Fe-NBC,on the anaerobic fermentation of microorganisms were studied.The maximum methane production of NDAC group and Fe-NBC group was(305.71 m L/g lactic acid)and(315.91 m L/g lactic acid)respectively,which was35.50%and 39.50%higher than that of blank group(226.48 m L/g lactic acid).Moreover,the maximum methane production rate of ndac group and Fe-NBC group increased from 59.253 m L/(g·h)to 82.914 m L/(g·h)and 98.378 m L/(g·h),respectively.The results show that both of them can effectively promote the rate and yield of methane production,and the effect of Fe-NBC group is the best.